I am aware that negative frequencies do not normally count towards the bandwidth when transmitting in the baseband. However when specifically asked to look at the null-to-null or zero-crossing bandwidth, should the negative frequencies count? For example, in the sinc plot below, is the bandwidth 1 or 2?

sinc plot

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    $\begingroup$ It's a matter of convention. I'd say the bandwidth is 1 in this case. Null-to-null is often used with bandpass signals or channels, where it makes more sense since the two nulls of interest are positive. $\endgroup$ – MBaz Sep 18 '19 at 2:02

It is null-null when the signal is bandpass and zero-null when the signal is baseband. So you will always take the positive frequencies.

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